DMF Week 5 SAQ

1

Which one of the time periods below best describes the timing of peak intensity of Type I hypersensitivity reactions:


  20 - 30 minutes

  6 - 12 hours

  12 - 18 hours

  1 - 2 days

  2 - 3 days


1 is correct: This is due to the release of pre-formed mediators.

2 and 3 are incorrect, although some mediators are produced at this time due to the activation of eosinophils. 4 and 5 are right out.

2

After activation, CD4 T cells may differentiate along several different pathways, two of which results in the production of TH1 and TH2 T cells. Which of the following statements is correct with regard to these differentiation pathways?


  TH1 T cells secrete interferon-gamma and activate mast cells

  TH1 T cell activation may result in eosinophil activation

  The production of interferon gamma and IL-12 induces TH2 differentiation

  IL-4 is produced by TH2 T cells and facilitates IgE production

  TH2 T cells are cytotoxic T cells that kill cells which have bound allergens

3

Which one of the statements below regarding mediators of Type I hypersensitivity reactions is correct?


  They are predominantly mediated by IgA secreted by plasma cells in submucosal tissues

  They are predominantly mediated by the release of complement components

  They are predominantly mediated by complement fixation on the surface of the mast cell which has bound antigen

  They are mediated by cross-linking of FcR on the surface of mast cells

  They are mediated by complexes of IgE and antigen which deposit in submucosal tissues

4

Which one or more of the following statements about eicosanoids is / are correct?

A: Increased generation of prostaglandins in inflammation is mainly due to the activity of cyclo-oxygenase-1

B: Inhibition of prostaglandin production is an effective treatment for allergic respiratory conditions

C: The production of prostaglandins is mainly restricted to leukocytes

D: Eicosanoid formation is normally limited by the amount of free arachidonic acid


  If A, B, and C, are correct.

  If A and C are correct.

  If B and D are correct.

  If D is correct

  If all are correct

5

Which one of the following statements about the mechanisms of T cell tolerance is incorrect?


  In the thymus, T cells with T cell receptors (TCR) which recognize self MHC- peptide complexes may be deleted during development.

  Self reactive T cells which survive thymic selection and enter the circulation may not cause damage in the absence of co-stimulation.

  Self reactive T cells which survive thymic selection and enter the circulation may not cause damage because their action is controlled by regulatory cells or cytokines.

  Self reactive T cells which survive thymic selection and enter the circulation may not cause damage because they are not able to gain access to the tissues for which they have receptors.

  It is very rare to find self reactive T cells in the circulation.

6

Which one of the statements about the mechanism of Type III hypersensitivity reactions is correct?


  Type III hypersensitivity arises because T cells respond to persistent antigens in an uncontrolled way.

  Type III hypersensitivity arises because antigen - antibody complexes are cleared from the circulation.

  Type III hypersensitivity arises because microbes fail to bind antibodies, and so persist in tissues.

  Type III hypersensitivity arises because antigen - antibody complexes deposit in the blood vessels and certain tissues.

  Type III hypersensitivity may be treated by administration of anti-histamines.

7

Which one of the following statements regarding autoimmune diseases is correct?


  Antibodies against intracellular antigens cannot cause damage to cells and tissues because antibodies cannot penetrate cells to access these antigens

  Patients with circulating autoantibodies will eventually suffer from autoimmune disease

  Organ specific antigens are not seen in the thymus hence T cells which react with these antigens cannot be deleted in the thymus.

  Autoantibodies produced against the acetylcholine receptor block the action of acetylcholine, resulting in Myasthenia gravis.

  Autoantibodies produced against thyroid stimulating hormone (TSH) mimic TSH and cause Graves disease.

8

Which one of the following statements regarding post-streptococcal immune damage is correct?


  Rheumatic fever may follow infection caused by a wide range of Str. pyogenes types.

  Post-streptococcal glomerulonephritis may follow infection caused by most sub-types of Str. pyogenes.

  Recurrence of post-streptococcal glomerulonephritis is prevented by long-term chemoprophylaxis with penicillin.

  Rheumatic fever is caused predominantly by Type IV (delayed type) hypersensitivity mechanisms

  Most people are susceptible to rheumatic fever following infection by Str. pyogenes